I got my wife's nissan murano cabriolet working with the iphone5 (ios 6.1.2 altough i don't think the ios version matters). It was previously working fine with an iphone 3GS, but as we all know when we got the iphone5, calls would be answered but then the radio would come on.
I have the iphone5 named as a single word (that may matter). The key thing was to turn off the "automatic hold" on answer feature in the car (see Rachmaninoff Piano Player's post above - but do the opposite; turn off the "automatic hold" on answer)
My guess is that in upgrading the bluetooth profile in the iphone5 Apple actually got the " transfer to hold" feature to work. With the older bluetooth profile the iphone wouldn't transfer to hold, so we could answer it in the car.
Your mileage may vary, but the fix above got my wife of my back about getting the iphone5/ fixed.
good luck!